Fixing complexity issue with f_equal. Thanks to J.-H. Jourdan

for reporting it.

A "cut" was not appropriately chained on the second goal but on both
goals, with the chaining on the first goal introducing noise.

2 files changed, 16 insertions, 2 deletions

diff --git a/plugins/cc/cctac.ml b/plugins/cc/cctac.ml
index 068cb25cf..371f76cf3 100644
--- a/plugins/cc/cctac.ml
+++ b/plugins/cc/cctac.ml
@@ -501,9 +501,9 @@ let f_equal =
     let concl = Proofview.Goal.concl gl in
     let cut_eq c1 c2 =
       try (* type_of can raise an exception *)
-        Tacticals.New.tclTHEN
+        Tacticals.New.tclTHENS
 	  (mk_eq _eq c1 c2 Tactics.cut)
-	  (Tacticals.New.tclTRY ((new_app_global _refl_equal [||]) apply))
+	  [Proofview.tclUNIT ();Tacticals.New.tclTRY ((new_app_global _refl_equal [||]) apply)]
       with e when Proofview.V82.catchable_exception e -> Proofview.tclZERO e
     in
     Proofview.tclORELSE
diff --git a/test-suite/complexity/f_equal.v b/test-suite/complexity/f_equal.v
new file mode 100644
index 000000000..30e87939e
--- /dev/null
+++ b/test-suite/complexity/f_equal.v
@@ -0,0 +1,14 @@
+(* Checks that f_equal does not reduce the term uselessly *)
+(* Expected time < 1.00s *)
+
+Fixpoint stupid (n : nat) : unit :=
+match n with
+| 0 => tt
+| S n =>
+  let () := stupid n in
+  let () := stupid n in
+  tt
+end.
+
+Goal stupid 23 = stupid 23.
+f_equal.